Monthly Archives: February 2016

Today I’m going to introduce you to the possibly most beautiful alga. Its name is Claudea elegans, which I adapted as “elegant claudea” to serve as a popular name.

I first became aware of the existence of such an organism in my childhood when I saw a drawing of it in an encyclopedia. It had a very beautiful shape, a nice pink color and a cute name. But it was simply depicted among several other algae on that page and besides the drawing and the name, nothing else was said.

Drawing of Claudea elegans from Phycologia Australica.

Unfortunately, there is not much information available online on the elegant claudea. It is a marine species found in Australia, Brazil, India, Pakistan and probably many other tropical waters around the world, being usually attached to rocks near sand and in places with a good current flow.

The net of the elegant claudea as seen under the microscope. The small sacs disrupting the net are the tetrasporangia, reproductive structures. Photo by Dr. Robert Ricker, NOAA/NOS/ORR.

It reaches up to 40 cm in height/length and is composed of branched stalks with a very peculiar pattern. The stalk has a sort of net on one of its sides that makes it look like a one-sided feather. The net is formed by many smaller stalks connected to each other by even smaller ones, one those again to each other by the smallest of all. The branches from the main stalk always come out from the opposite side of the net and have themselves a net on one of its sides and smaller stalks growing opposite to it. The elegant claudea is, therefore, somewhat a double fractal.

As you can notice, Linnaeus’ classification of amphibians and fish was even worse than that of mammals and birds, especially the classification of amphibians. It is clear that Linnaeus hated what he called amphibians more than anything. He describes them as the worst creatures, having a horrible appearence, and thanking God for not creating many of them.

Probably one of the most bizarre things is that Linnaeus put lizards and crocodiles in the same genus! Well, if he hated “amphibians” so much, I think he was not very familiar with their anatomy.

I think most of us know already that the largest animal ever is our beloved blue whale, Balaenoptera musculus. It can reach 30 m in length and weigh more than 180 tonnes. It’s really big, but probably not as big as many people think. There are some popular legends, like that the heart of a blue whale is the saze of a car or that a human could swim inside its aorta, which are not actually true.

It’s almost impossible to find a good photo of the entire body of a blue whale. Afterall, it’s huge and lives underwater!

But what else can we say about the blue whale? It is a rorqual, a name used to designate whales in the family Balaenopteridae and, as all of them, its main and almost exclusive food is krill, a small crustacean very abundant in all oceans. And krill needs to be abundant in order to provide the thousands of tonnes that all whales in the oceans need to eat every day. A single blue whale eats up to 40 million krill in a day, which equals to roughly 3.5 tonnes. A blue whale calf (young) is born measuring around 7 m in length and drinks around 500 liters of milk per day!

Blue whales were abundant in nearly all oceans until the beginning of the 20th century, when they started to be hunted and were almost extinct. Nowadays, the real population size is hard to estimate, but may encompass as few as 5,000 specimens, much less than the estimated hundreds of thousands in the 19th century. Due to such a drastic reduction in the population, the blue whale is currently listed as “endangered” in IUCN’s Red List.

But let’s see a blue whale in all of its blueness.

Occasionally, blue whales can hybridize with fin whales (Balaenoptera physalus) and perhaps even with humpback whales (Megaptera novaeangliae), a species classified in a different genus! Some recent genetic analyses, however, indicate that the Balaenoptera genus is polyphyletic and the blue whale may become known as Rorqualus musculus.

Different from other whales, blue whales usually live alone or in pairs, but never form groups, even though they may sometimes gather in places with high concentrations of food.

Like other cetaceans, especially other baleen whales, the blue whale sings. The song, however, is not as complex and dynamic as the ones produced by the related humpback whale. An intriguing fact that was recently discovered is that the frequency of the blue whale song is getting lower and lower at least since the 1960s. There is no good hypothesis to explain this phenomenon yet, but several ones have been proposed, such as the increase in background noise due to human activities or the increase in population density due to the decrease in whaling.

When it comes to nature, people are always curious about the superlatives, the extremes. What’s the largest, the smallest, the oldest, the most venomous… But there’s another extreme that people usually don’t think about: the leggiest!

So today we’ll talk about it. The leggiest animal, i.e., the animal with the largest number of legs.

Its scientific name is Illacme plenipes and it lacks a common name, so I decided to call the “leggiest millepede”, since that’s what it is. The name “millipede” means “a thousand feet”, but none of them actually reach that number. I. plenipes, however, comes pretty close, having as much as 750 legs! It is so long and so leggy that watching it move is almost a torture.

A female Illacme plenipes. Photo from Marek et al. (2012).*

This species was described in 1928 from a small locality in California and is so rare that it wasn’t found again for almost 80 years, being rediscovered only in 2005 in an area close to the original one. Despite having hundreds of legs, it is a very small species, being less than 4cm long. Most examined species have less than 700 legs because of the unusual development found in most or all millipedes.

Like all arthropods, millepedes shed their exoskeleton from time to time to allow them to grow. In millipedes, every time they shed, they increase the number of body segments and legs. It continues throughout their lives, even after becoming sexually mature. Therefore, we could even find some specimens having more than the record of 750 legs!

So, let’s start again with Linnaeus, more precisely with the 10th Edition of his work Systema Naturae. This edition is the starting point of zoological nomenclature and was published in 1758.

In the Systema Naturae, Linnaeus divided “nature” in three kingdoms: Regnum Animale (animal kingdom), Regnum Vegetabile (vegetable kingdom) and Regnum Lapideum (mineral kingdom). As minerals are not lifeforms, we’ll not deal with it here, since this classification does not make sense at all for rocks. Maybe I’ll talk about it later in another post.

At first I would present the whole system here, but the post would become too big. Therefore, I decided to present animals and plants separately, but again there was too much to talk on animals. So, this post will deal only with mammals and birds. Other groups will be presented in subsequent posts. See amphibians and fish here, insects here and worms here.

Animals were defined by Linnaeus as having an organized, living and sentient body and being able to move freely. They were classified in six classes: Mammalia, Aves, Amphibia, Pisces, Insecta and Vermes.

1. Mammalia (Mammals)

Heart with two auricles and two ventricles; warm red blood.Lungs breathing reciprocally.Jaw incumbent, covered.Penis entering in viviparous, lactating.Senses: tongue, nostrils, touch, eyes, ears.Covering: hairs, few for the Indic ones, fewest for the aquatic ones.Support: four feet, except for the aquatic ones, in which the posterior feet coalesced with the tail.

Mammals included 8 orders that were defined mainly on the arrangement of teeth: Primates, Bruta, Ferae, Bestiae, Glires, Pecora, Belluae, and Cete. They are shown below with their respective genera.

The order Cete included the following four species (left to right): narwhal (Monodon monoceros), bowhead whale (Balaena mysticetus), sperm whale (Physeter macrocephalus) and common dolphin (Delphinus delphis).

Spider are famous for being horrible creatures, atrocious predators with terrible venom and creepy webs. But that’s not quite true once you start to know them well, but, anyway, they used to be considered a group of animals composed solely by predators.

That’s not true anymore. In 2008, it has been found that a small jumping spider is predominantly vegetarian! Its name is Bagheera kiplingi, or the Kipling’s Acacia Spider, and it is our newest Friday Fellow.

The Kipling’s Acacia Spider is found in Central America, in Mexico, Costa Rica and Guatemala. It’s a jumping spider (family Salticidae), the most diverse family of spiders.

Living on acacia trees, the Kipling’s Acacia Spider feeds mainly on Beltian bodies, small structures at the tip of the Acacia’s leaflets that are rich in proteins, sugars and fats. The Beltian bodies are a food source for ant species of the genus Pseudomyrmex that live in a mutualistic relationship with the acacias, protecting the trees from herbivores.

Our spider most likely became an oportunist by exploring a resource that was not designed for it. And more than that, sometimes the spider can attack and eat the ants, especially their larvae, so becoming a kind of annoying disturbance to the mutualistic relationship between ant and tree.

However, despite the fact that it also feeds on ant larvae, Bagheera kiplingi has the Beltian bodies as its main food source. Ironically, the name Bagheera comes from Rudyard Kipling’s character Bagheera, which is a black panther. The specific epithet, kiplingi, honors Rudyard Kipling himself.

Warm blood is the popular way to refer to endothermy, the ability that certain animals have to maintain a high body temperature by the use of heat generated via metabolism, especially in internal organs. Mammals and birds are the only extant groups in which all representatives are endothermic, but some fish also have this feature.

Tunna fish are truly endothermic fish, similar to mammals and birds. Photo by opencage.info**

In order to maintain a high body temperature, endothermic animals need a much higher amount of daily food than ectothermic animals (the ones that rely on environmental sources to adjust their body heat). There must be, therefore, a considerable advantage in endothermy to explain such a increased consumption of resources. The advantages include the ability to remain active in areas of low temperature and an increase in efficienty of enzimatic reactions, muscle contractions and molecular transmission across synapses.

The origin of endothermy is still a matter of debate and several hypothesis have been erected. The main ones are:

1. A migration from ectothermy to inertial homeothermy and finally endothermy.

According to this hypothesis, animals that were initially ectothermic grew in size, becoming inertially homeothermic, i.e., they retained a considerable constant internal body temperature due to the reduced surface area in relation to the their volume. Lately, selective pressures forced those animals to reduce in size, which made them unable to sustain a constant internal temperature and therefore their enzimatic, muscular and synaptic efficiency became threatened. As a result, they were forced to develop an alternative way to maintain a high body temperature and acquired it through endothermy.

Initially considered a plausible explanation due to the body size of the ancestors of mammals in fossil record, new phylogenetic interpretations caused a complete mix of large-bodied and small-bodied animals, so that currently fossils don’t support this idea anymore.

2. A large brain heating the body

The brain in endothermic species produces much more heat than any other organs. This led to the assumption that maybe a large brain generating heat was the responsible for the later development of full endothermy. However, evidence from both exant and extinct species point to the opposite. It seems more reasonable that a large brain evolved after endothermy and not the opposite.

3. A nocturnal life needs more heat

This idea states that the development of endothermy happened as a way to allow animals to be active during the night. The fact that most primitive mammals appear to have been nocturnal seems to support this hypothesis, but in fact many extant nocturnal mammals actually have a lower body temperature than diurnal mammals. Other aspect that counts against this hypothesis is that the ancestors of mammals already showed evidences of an increase in body temperature despite the fact that they most likely were not nocturnal.

4. Heat to help the embryos to develop

As you may know, in many ectothermic vertebrates, such as reptiles, eggs need to be incubated at a constant temperature in order to develop adequately. Endothermy, therefore, could have evolved as a way to allow parents to incubate the eggs themselves and have a higher control on temperature stability. One fact that support this theory is the dual role of thyroid hormones in reproduction and in the control of metabolic rate.

Endothermy may have evolved to incubate eggs at a constant temperature. Photo by Bruce Tuten**

5. Aerobic capicity leading to the heating of internal organs

According to this hypothesis, endothermy evolved after the increase of aerobic capacity, i.e., the first thing to happen was to increase the ability of muscles to consume oxygen in order to release energy, which helped the animal to move faster, among other things. This increased aerobic capicity was attained by increasing the number of mitochondria in muscle cells, which led to higher body temperature in the muscules and consequently a higher visceral temperature. Despite fossils indicating that mammal ancestors developed morphological adaptations indicating increased aerobic capacity, it is not possible to afirm that endothermy was not already present in those species.

Very recently, it has been found that the tegu lizards (Salvator merianae) from South America increase their body temperature during the reproductive season, achieving as much as 10°C above the environment temperature at night. Thus, it seems that they are able to increase heat production and heat conservation in ways similar to the ones used by fully endothermic animals.

The tegu lizard Salvator merianae is a facultative endotherm. Photo by Jami Dwyer.

As such an increase in body temperature happens during the reproductive cycle, it supports the hypothesis of endothermy evolving to assist the development of embryos, as explained above. Also, it indicates that ectotherms may engage in temporary endothermy and perhaps permanent endothermy may have evolved by using this path.

Further studies on the tegu lizards are needed to clarify this interesting phenomenon and expand our knowledge on endothermy evolution in mammals and birds.